Process for fireproofing cellulosic materials



Patented Oct. 15, 1935 UNITED STATES PATENT OFFICE Martin Leatherman, Hyattsville, ma; dedicated to the free use of the Public of the United States of America No Drawing. Application February 17, 1934,

Serial No. 711.727

' 3' Claims. (CI. 91-08;

(Granted under the m of March}, 1883, as amended Apr-i130, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928 and the invention herein described, if patented, may be manufactured and used by or for the 5 Government for governmental purposes without the payment to me of any royalty thereon.

I hereby dedicate the invention herein described to the free use of the public in the territory of the United States of America to take effect upon the granting of a patent to me.

This invention relates to an improvement in the fireproofing of cellulosic materials which also largely prevents the out-of-door deterioration of cellulosic fabrics arising from the effects of certain general classes of treating materials, when acted upon by sunlight.

It is well known that hydrated stannic oxide prevents flaming of cellulosic materials when properly placed therein. However, it has never been established as to why or how stannic oxide inhibits flaming of cellulosic fabrics when the said fabrics are exposed to an igniting flame. I have discovered the mechanism involved in this said flame-proofing process and in order to make these specifications as complete as possible I will briefly describe my discoveries and also the manner in which these discoveries were authenticated.

The three lines of. investigation which I followed all tended to prove that stannic oxide 3 flameproofs cellulose by setting up a catalytic dehydration of the cellulose under the influence of heat. In the first place, when untreated fabric samples and flameproofed fabric samples were respectively heated in tubes at 325 C. in a stream of dry, COzfree air, the exit gases obtained from the flameproofed fabric samples invariably showed much the larger percentage of C02. The samples in all cases were completely ashed before the air flow was stopped. The air and the gases swept out with it were all collected in a large evacuated bottle each time, and aliquot samples of the collected gas were analyzed in a modified Orsat apparatus. The larger yield of CO: from the treated samples indicated to me that with the treated, fiameproofed samples the products formed were largely C02 and water, whereas with the untreated samples the carbon was evolved as a constituent of volatile combustible compounds such as acetone, hydrocarbons, etc.

In the second phase of my investigations the carefully dried fabric samples were heated in tubes "in a stream of dried oxygen-free nitrogen, the tubes being immersed in a molten metal bath at 325 C. for 240 seconds. The tarry matter was 56 filtered out of the exit gases and the evolved moisture was collected and weighed. The percentage of water evolved, based on the net weight of the fabric, was always much greater in the case .of the samples treated with stannic oxide.

The third line of study was undertaken to es- 5 tablish beyond any doubt that the stannic oxide effects its flameproofing action by splitting the cellulose into carbon and water. Treated and untreated samples were heated at 325 C. in tubes in a stream of dried oxygen-free nitrogen until 10 most of the matter volatile at that temperature was driven off, the heating being continued the same length of time in all cases. The container tubes were then connected with an absorption train and the fabric residues were completely 16 burned in a stream of oxygen. .In this way the carbon in the residues was determined as carbon dioxide. Based on the net weight of carbon in the original cellulose of the fabric samples, the percentage of carbon in the residues from the 20 destructive distillation of the treated fabric was nearly twice as great as in the identically obtained residues from the untreated fabric.

Thus it was definitely proved that stannic oxide flameproofs cellulose by catalytically splitting the 25 I cellulose carbohydrate into carbon and water and thereby preventing the formation of combustible gases. It now became possible to improve the action of stannic oxide by applying known principles of catalysis. In the first place, it has been 30 shown by others that alkali acts as a catalyst poison. Therefore, if it were possible to precipitate stannic oxide in the cotton fabric under more acid conditions a more pronounced flameproofing eflect should be produced. The Perkin method, 5 Patent No. 856,906, of using fairly dilute ammonium sulfate solutions to decompose the sodium stannate on the fabric precipitates the. stannic oxide under alkaline conditions because of the ammonia evolved. 40

If, for example, instead of using ammonium sulfate as the precipitant for sodium stannate, ferric sulfate or chloride is used, three effects are obtained. In the first place a solution of ferric sulfate or of ferric chloride is acid in reaction, as 45 is ammonium sulfate, because of hydrolysis.

The reaction between sodium stannate and the ferric salt, if an excess of the latter is used, leaves the solution from which the stannic oxide is deposited still acid, unlike ammonium sulfate, and 60 this lessens. the quantity of alkali which can be absorbed by the freshly precipitated, gel-like stannic oxide. In the second place, ferric oxide is precipitated in intimate contact with the stan-.

nic oxide and thereby exerts catalytic promoter eflects. Many other oxides exert similar effects. In the third place, and most important, the iron oxide colors the fabric and this coloring exerts a preservative action on the fabric. This is true of other colored oxides such as those of chromium, manganese, copper, cobalt, nickel, etc. Stannic oxide alone in fabric accelerates deterioration of cotton fabric in sunlight;

The desirable catalytic action of stannic and other oxides in flameproofing of cellulose is accompanied by a most undesirable action. These oxides are also catalysts for carbon combustion and after the dehydration mechanism liberates the carbon the oxide facilitates its combustion.

Consequently flameproofed fabrics glow vigorously even though they do not flame. For this reason, to produce a fully fireproofed fabric, after flameprooflng with metallic oxides, it is necessary to use a supporting agent. From the standpoint of weather-resistance there is only one type of material which will suffice. This type of material is represented by chlorinated organic substances of various kinds. It is known to use the chlorinated vinyl resins in combination with tin oxide, but, while this treatment effectively flreproofs cotton, it is impracticable because both stannic oxide and chlorinated vinyl resin act very destructively on the fabric so that the fabric lasts only a short time. However, I have discovered that this destructive action is. prevented by the presence of a coloring material.

In the past, the chlorinated resinous materials have all been objectionable because of cost or undesirable physical or chemical properties. I have found that certain cheap petroleum derivatives can be chlorinated to give materials which are very well suited as glowprooflng agents for use in connection with oxide mixtures in cellulose fabrics for exposure to weather. The glowproofing effect results from the evolution of hydrogen chloride at elevated temperatures. The chlorinated product must not decompose spontaneously when properly protected, that is, by a coloring material, and it must evolve hydrogen chloride within a definite temperature range. I have discovered that highly chlorinated paraflln wax answers these requirements but does not have the desired physical properties, that is, it stiifens the fabric too much. If, before chlorination, I mix withthe paraffin approximately its own weight of certain light bodied partially unsaturated liquid paraflln oils of low lubricating power, such as are used by filling stations for flushing crank cases, I can introduce a higher percentage of chlorine and still obtain a less plastic product which does not unduly stiffen the fabric but results in a flexible, soft, flre-proofed material which is also highly water proofed. I prefer to have in the finished chlorinated material flfty to seventy per cent of chlorine based on the total weight of product but the percentage of chlorine may, within the spirit of my invention, be less or more than this.

It is well known that tin is a rare metal and that its cost must progressively increase. One of the further merits of my invention lies in the fact that by using promoter oxides, a part of the tin necessary for fiameprooflng may be replaced with cheaper metal oxides. An additional merit of my invention lies in the possibility of assisting, without deleterious results, the fiameprooflng efiect of the oxides by using the above-mentioned resinous chlorinated petroleum derivatives, which besides glowproofing the fabric, markedly assist in flreprooflng it.

.fate.

aornaos A typical procedure which I may follow in producing a weather-resistant flreproofing treatment in cellulose fabrics is as follows: if the fabric is unbleached and water-resistant it is first soaked in a solution of a'wetting agent of either the sul- 5 fonated type or of the sulfate ester type for about five minutes, such as a one per cent aqueous solution of a metallic salt of a sulfate ester of an aliphatic alcohol, then squeezed out and rinsed thoroughly in water for aboutflve minutes, after which it is again squeezed out and immersed in sodium stannate solution for about twenty minutes. When bleached and absorbent fabric is being treated the wetting agent treatment is unnecessary. The sodium stannate solution con- 15 tains about twenty parts or less of alpha sodium stannate 'in one hundred parts of water. The fabric is dried by any suitable means after soaking-in the stannate solution and then put into a twenty per cent aqueous solution of ferric sul- 20 This produces a tan colored fabric; Instead of iron salts, such salts as chromium sulfate, manganous sulfate, vanadium chloride,-titanous sulfate, or any salt of a strong mineral acid with a weakly base-forming metal, the hy- 25 droxide of which is water-insoluble, may be used. Where the precipitating salt does not leave a colored precipitate, as in the case of titanium or vanadium salts, it is necessary to use a previously colored fabric or to introduce a pigment later, 30 preferably with the resin treatment. It may also be desirable to mix enough iron or chromium salt with the titanium salt solution to produce a colored precipitate in the fabric. 1

After the precipitation of the stannate the fabric is washed without previous drying in order to remove acid residues and is then dried. It is then ready for the treatment with the glowproofing agent.

As a typical composition of the glowproofing 40 resin solution I may use 180 grams of chlorinated petroleum products, preferably a chlorinated mixture of paraflin and light bodied unsaturated petroleum oils containing about 60 "per cent of chlorine based on total weight, 30 grams of triphenyl phosphate and 20 grams of beeswax in 550 grams of carbon tetrachloride. This glowproofing solution leaves in the lightly squeezed fabric after evaporating off the solvent, material amounting to about 30 per cent of the total treated weight of the fabric. The oxide treatment 'will amount to about 10 per cent of the combined weight of fabric and oxides. The triphenyl phosphate acts as a plasticizer and the beeswax acts as a waterproofing agent as well as to improve the feel of the goods.

These proportions may be varied considerably. For example, if the percentage of flameproofing oxide is increased the percentage of glowproofing agent can be decreased to a certain point. The

plasticizing agent may be changed and the amount of beeswax altered or omitted. Also the glowprooflng solution may be made the vehicle for a pigment, and a paint thereby prepared which is especially useful in preparing striped awnings and the like. In such a case it may be desirable to change the solvent and substitute any other compatible organic solvent. As pigment any earthy material such as ochre, umber, sienna, etc., or any colored metallic oxide may be used.

In the treatment outlined above there is no water-soluble constituent which can be leached out by rain, and the pigmenting material stabilizes the chlorinated resinous product. The fabric retains its fireproof characteristics and does not rapidly lose its tensile strength as it will do when no pigment is present.

The petroleum hydrocarbons furnish a cheap source of raw material for chlorination and the finished chlorinated product is cheap enough to be used in low priced fabrics.

Having fully disclosed my invention, I claim:

1. The process of fire-proofing and preserving cellulosic materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent aqueous solution of a metallic salt of a sulfate ester of an aliphatic alcohol, rinsing the cellulosic material thoroughly in water, pressing out as much of the water as possible; then impregnating the cellulosic material with sodium stannate, drying, and then immersing the dried cellulosic material in a water solution of a. salt of a strong mineral acid with a weakly base-forming metal, the hydroxide of which is water-insoluble, then washing the material in water to remove acid residues, drying the material, impregnating the material with chlorinated petroleum derivatives and incorporating in the resulting cellulose fabrics coloring materials.

2. The process of fire-proofing and preservin cellulose materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent solution of a metallic salt of a sulfate ester of an aliphatic alcohol, rinsing the cellulosic material thoroughly in water, pressing out as much of the water as possible; then im-' pregnatlng the cellulosic material with sodium st'annate, drying, and then immersing the dried 5 cellulosic material in an aqueous solution of ferric sulphate, then washing the cellulosic material in water to remove acid residues, drying the cellulosic material and impregnating it with chlorinated petroleum derivatives. 10

-3. The process of fire-proofing and preserving cellulosic materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent aqueous solution of a metallic salt 01 a sulfate ester of an aliphatic alcohol, rins- 15 ing the cellulos'ic material thoroughly in water, pressing out as much of the water as possible; then impregnating the cellulosic material with sodium stannate, drying, and then immersing the dried cellulosic material in a water solution of a 20,

salt of a strong mineral acid with a weakly baseforming metal, the hydroxide of which is waterinsoluble and colored, then washing the material in water to remove acid residues, drying the material and impregnating'the material with a 25 chlorinated mixture of pa'raffln wax and light bodied partially unsaturated petroleum oils.

MARTIN LEATHERMAN. 

